Internal combustion spark ignition engines require varying amounts of air so as to idle properly under various operating conditions. As examples, (1) an increased amount of air is required when an engine is idling "cold" as compared to the amount of air required for proper idling of a "warm" engine; (2) an extra amount of air for emission reasons is required under conditions of deceleration, and (3) the amount of air flow must be varied so as to maintain relatively constant idle speed when loads on the engine (such as air conditioning compressors, alternators, etc.) are cycled.
Internal combustion engines have become increasingly more sophisticated with the use of microprocessor-based engine control units (ECU). For example, the ECU may typically receive data corresponding to engine temperature, engine speed, manifold pressure, oxygen content in exhaust gases as well as other conditions, for example, closed throttle (i.e. full choke) conditions on start up and the like. This data is then assimilated by the ECU and is used for various purposes, one of which is to operate conventional idle control assemblies, such as those represented by U.S. Pat. No. 4,539,955 issued to Robert E. Wilson et al on Sept. 10, 1985, and U.S. Pat. No. 4,212,272 issued to Rufus L. Hawk on July 15, 1980, each being entitled "Idle Speed Control Device for Internal Combustion Engine".
According to these prior idle control assemblies, the signals are received fron the ECU in the form of reverse polarity DC voltages so as to actuate a motor which, in turn, increases/decreases the length of a shaft having an end in contact with the throttle valve linkage. These types of devices, therefore depend upon automatic opening and closing of the throttle valve--that is, the throttle valve itself is opened (or closed) in dependence upon the operating conditions of the engine sensed by the ECU. While this functioning may be adequate for some engine operating conditions (such as "cold" engine operation), it cannot function as a means for controlling the quantity of air introduced into a throttle bore independently of the particular throttle valve setting.
Another conventional air control valve is disclosed in U.S. Pat. No. 4,369,755 issued to Masaaki Saito on Jan. 25, 1983, entitled "Air Control Device". This prior control valve is positioned in an air passage bypassing the throttle valve and thus operates independently thereof. A D.C. motor is connected to an inner cylindrical body in such a way that the latter can be rotated by the former. Rotation of the inner cylindrical body relative to an outer cylindrical body thus controls the amount of air flowing through the air passage bypassing the throttle. No means are disclosed in U.S. Pat. No. 4,369,755 however, which mechanically "decouples" the D.C. motor and the inner cylindrical body in response to a threshold torque being exceeded. Thus, the provision of a rotation angle sensor and a motor disabling circuit appear to be requirements of the valve of U.S. Pat. No. 4,369,755 during use since damage to the motor and/or inner cylindrical body could ensue without such electronic safeguards when the inner cylindrical body achieves its maximum (minimum) rotational position.
A balanced dual valve air flow regulator is disclosed in U.S. Pat. 4,421,083 issued to Donald D. Stoltman on Dec. 20, 1983, entitled "Engine Air Flow Regulator". According to this prior patent, the ECU varies the duty cycle of a solenoid so as to correspondingly vary air flow past valve seats until pressure on one side of a diaphragm balances the diaphragm force with the bias of the solenoid. In such a manner, air flow control through a throttle bypass control may be accomplished independently of throttle position.